Many people suffer from an inability to control urinary function, i.e., urinary incontinence. Different muscles, nerves, organs and conduits within the urinary tract cooperate to collect, store and release urine. A variety of disorders may compromise urinary tract performance and contribute to incontinence. Many of the disorders may be associated with aging, injury or illness. For example, aging can often result in weakened sphincter muscles, which cause incontinence, or weakened bladder muscles, which prevent complete emptying. Some patients also may suffer from nerve disorders that prevent proper triggering and operation of the bladder or sphincter muscles.
One common form of urinary incontinence, referred to as “stress incontinence,” is attributable to a failure of muscles around the bladder neck and urethra to maintain closure of the urinary outlet. Patients with stress incontinence may experience minor leakage from physical activities that apply pressure to the bladder, such as coughing, sneezing, laughing, exercising or other movements that increase intraabdominal pressure. Another common form of urinary incontinence, referred to as “urge incontinence,” (also called hyperactive or overactive bladder) involves the involuntary leakage or urine while suddenly feeling the need or urge to urinate. Urge incontinence may attributable to abnormally heightened commands from the spinal cord to the bladder that produce unanticipated bladder contractions, or from damage to the nerves of the bladder, nervous system or the muscles. Patients with urge incontinence need to urinate frequently. When the bladder reaches capacity, the nerves appropriately signal the brain that the bladder is full, but the urge to void cannot be voluntarily suppressed.
Electrical stimulation of nerves in the pelvic floor may provide an effective therapy for a variety of disorders, including urinary incontinence. For example, an implantable electrical stimulator may deliver stimulation to treat urinary incontinence. The electrical stimulator may be a neurostimulator that delivers electrical stimulation to the sacral nerve to induce sphincter constriction and thereby close or maintain closure of the urethra at the bladder neck. In addition, electrical stimulation of the bladder wall may enhance pelvic floor muscle tone and assist fluid retention in the bladder or voiding fluid from the bladder. An appropriate course of electrical stimulation therapy may be aided by a sensor that monitors physiological conditions of the bladder. In some cases, an implantable stimulation device may deliver stimulation therapy based on the level or state of a sensed physiological condition.